The present invention relates to a multi-axis robot represented by an industrial robot having a dynamic interaction between mutual control axes which includes a spring element in each axis, and particularly to a controller thereof for entirely removing the interaction force produced at the top end of an arm.
In general, in an industrial robot where each axis is driven by a motor, in order to ideally reduce influences of a lack of power of the motor or a disturbance from a load side, an arm at the load side is driven through a gear such as a harmonic drive having a high reduction ratio. Consequently a dynamic interaction between the control axes does not become a problem in the prior art.
However, accuracy as demand increases for higher speed and accuracy dynamic influences which cannot be compensated for by the PI control, and disturbances which cannot be neglected even with the high reduction ratio are produced.
In order to solve these problems, a method of compensating for the disturbance by use of a disturbance estimation observer and a method of previously compensating for the disturbance based on a dynamic equation in a similar manner to a robot of a direct drive system have been reported (e.g., Japanese Patent Laid-Open No. 63-314606, Japanese Patent Laid-Open No. 6-270079, and Japanese Patent Laid-Open No. 7-7307).
When the disturbance produced at the load side is large, with the disturbance compensation observer method, sufficient improvement in accuracy cannot be expected because the dynamic property regarding the interaction or the like is not considered Also, regarding the method of previously compensating for the disturbance based on the dynamic equation, in the conventional method, the dynamic property involving interposing a gear or the interaction force including the control input calculated to operate each axis is not sufficiently considered, so that the interaction cannot be completely removed during high speed operation.